Incentives which could include a take-home dose of methadone or access to a rapid dosing line, would be given when, for example, a blood sample comes back negative for cocaine or non-prescription opiates.

NICE says giving privileges to reinforce positive behaviour is already used in drug management in the UK, if inconsistently.

Under the voucher scheme, the monetary value of the vouchers would increase up to £10 with each successive negative test, but fall back to a baseline value of £1.50 after a positive test.

Tests should be carried out three times a week for the first three weeks, twice a week for the following three weeks and once a week thereafter until stability is achieved. It would be advisable only to remove incentives when a patient is stabilised. It is important that they are involved in decision-making over their care.

Consultation is open until 5 March, with the final guideline expected in July.